The AV access strategy at LKH Feldkirch focusses primarily on utilising native fistula and Duplex mapping of the upper extremity is undertaken to identify the most appropriate approach.
AV grafts are only used in patients not suitable for a native fistula.
Conventional AV grafts typically require one to two revisions per year.
Since September 2010, a series of 16 grafts have been implanted in 15 patients. All patients have had previous
surgery (mean of 4.3 previous procedures (0-24). Mostly loop grafts in the forearm are utilised.
• 11 loop forearm
• 2 loop upper arm
• 2 straight upper arm
• 1 loop thigh
• 4 graft occlusions / two successful thrombectomies
• 4 graft explants (2 due to steal, 2 due to infection)
The results from 16 Spiral FlowTM AV Grafts, implanted between September 2010 and August 2013 were reviewed. Median follow up was 22 months and all grafts were Duplex scanned every three months to confirm the presence of Spiral Flow. Additional scans were performed if there was any suspicion of graft failure.
At 22 months, the primary rate was 72%; secondary patency was 85.5%
The results were compared to a series of 79 conventional PTFE grafts implanted by Dr Hofmann between January 2005 and December 2009. A Kaplan-Meier analysis highlighted primary patency rates at 18 months of 72% for Spiral FlowTM and 36.7% for conventional PTFE grafts. (P=0.01)
Changing the flow pattern at the venous anastomosis of AV grafts using the Spiral Flow Technology seems to be a simple but valuable tool in order to improve patency rates of PTFE AV grafts
The aim of this single centre study was to compare the primary and secondary patency rates at one year of conventional PTFE infrainguinal bypass grafts with a new Spiral Laminar Flow ePTFE graft.
Prospective data on primary and secondary patency rates and interventions/complications was gathered on 68 infrainguinal bypasses using Spiral Flow Grafts from February 2011 to October 2014. The data on 136 standard grafts was gathered retrospectively on all infrainguinal PFTE grafts over a six year period from Jan 2003 to Dec 2008. Data was obtained from case notes and surveillance scans. There were no changes in case mix or operative/interventional procedures between the two groups/time periods. Data was also obtained on type of operation, mortality and amputation rates. At one year, data for 54 Spiral Flow Grafts and 124 standard grafts was available for review.
| ||Spiral Flow||Conventional ePTFE
|Age||69.6 mean (47-92)||70.3 (45-93)
|Sex||78% male||48% male
Level of Implantation
| ||Spiral Flow||Conventional ePTFE
|Below Knee / Tibial / Complex||52%||87%
Vein cuffs were added to all BK/distal anastomoses.
Spiral Flow was seen on post-operative imaging at all distal anastomoses and run-off vessels.
Primary patency (Actuarial %)
| ||Spiral Flow||Conventional ePTFE
|Below Knee / Tibial / Complex||61%||48%
Secondary patency (Actuarial %)
|Below Knee / Tibial / Complex||79%||53%
Benchmarked against conventional grafts highlights a 30% actuarial improvement in primary and secondary patency. Results out to 3 years, particularly of more complex grafts, would appear to indicate a sustained patency advantage over conventional grafts. Significantly encouraging initial results to warrant continued usage and further long term data acquisition.
AV access grafts are used in those patients where there are no available superficial veins for native AV fistula creation. Their usable life and patency rates are far from being ideal requiring frequent interventions to maintain their use for dialysis. Their failure is usually related to neointimal hyperplasia leading to stenosis of the venous outflow near the venous anastomosis. Studies have shown that, Spiral laminar flow is the normal pattern of flow in most of the large and medium sized vessels in vivo as well as many functioning native AV fistulas. The Spiral flow graft has a design that creates a spiral laminar flow at the venous end that is a hypothetically reduces intimal hyperplasia and graft failure. We here report the midterm results of the largest reported series of using the graft in AV access.
Material & Methods
After IRB approval, a prospective study of using Spiral Flow graft for AV access in our institution between Jan 2012 to Dec 2014 was performed. Enrolled patients had no suitable superficial veins for native AV fistula creation. Patient demographics and comorbidities were recorded.
Kaplan Meier curve analysis was used to calculate patency rates compared to historic controls of straight ePTFE and heparin bonded grafts in our institution.
Complications were also recorded.
48 cases were included. The access site was the upper arm (32), the forearm (13), and chest wall (3). Mean age of 61 and mean follow up of 14 months. At 12 month, the assisted primary and secondary patency rates were 70% and 82%, respectively that was significantly better than historic controls using straight ePTFE and heparin bonded grafts in our own institution.
Complications included 4 graft infections; 3 severe steal syndrome, 4 seromas and 3 arm swelling. There were only 2 early graft failures.
Spiral flow grafts are a valid successful option for AV access. One year results are superior to using straight ePTFE and heparin bonded grafts. This may be explained on the basis of the hemodynamic environment created by the spiral laminar flow and may be a significant contribution to preventing neointimal hyperplasia and hence AV access graft failure.
A palpable “thrill” is traditionally associated with success following arteriovenous fistula (AVF) surgery. A thrill typically characterizes turbulent flow and this is a paradox as turbulence is a driver of neointimal hyperplasia. Spiral laminar flow (SLF) has been described as normal and protective pattern of flow in native arteries and is associated with superior patency in bypass grafts that generate it. The aim of this study was to define the pattern of flow within AVFs immediately post-operatively and at follow-up to assess maturation.
Doppler ultrasound was used immediately post-operatively and at follow-up (6 weeks). Blood flow was assessed as SLF or non-SLF. Two blinded qualified observers analysed the images. Patients were followed up for 6 months. Maturation was statistically analysed against the type of flow.
Sequential patients having AVF surgery (n=56) were assessed: 46 (82%) patients had a thrill, 3 patients had no flow and 7 patients had pulsatile flow without a palpable thrill. SLF was present in 80% of those with a thrill but not in any without a thrill (p<0.0001). At follow-up (n=51) 41, patients had a matured AVF (80%), of which 76% had SLF immediately post-operatively. Only one patient with SLF failed to mature. In the non-SLF group 5 of the 15 AVFs failed to mature (66%; p<0.005).
SLF was strongly supportive of successful fistula maturation. A “thrill” was characteristic of spiral rather than turbulence. The mechanism of this apparent beneficial effect of this pattern of flow requires further investigation.
A peripheral vascular graft is used for the treatment of peripheral arterial disease. Restenosis in the distal anastomosis is the main reason of occlusion and is related to haemodynamics. Single spiral flow is a normal feature in vessels. A graft designed to generate a single spiral in its outflow (VFT Ltd, Dundee, UK) has been introduced in clinical practice. This study compared the spiral graft with a control non-spiral using image-guided modelling.
Both grafts were housed in ultrasound flow phantoms. Anastomotic angle θ was applied at 20°, 40°, 60° and 80°. The phantoms were scanned with CT (Biograph mCT, SIEMENS, Germany) and the graft-vessel mimic lumen geometry was extracted with Amira (FEI Visualization, France). Based on these geometries volume meshes were created (ICEM CFX, ANSYS, Canonsburg, USA), which consisted of tetrahedral cells in the core and prismatic cells in the wall boundary. Mesh independence tests were applied based on maximum wall shear stress and velocity.
The blood was assumed Newtonian, homogeneous and incompressible, the walls rigid and the inflow a steady parabola (Reynolds 620, 935). The Navier-Stokes governing equations of flow were solved with ANSYS CFX.
Fluid dynamic parameters were compared between the spiral and corresponding non-spiral models focusing on the flow downstream of the anastomosis.
The vortical structures at cross-flow patterns 1-4 had previously been studied experimentally with ultrasound vector Doppler imaging, which was used for validation.
The presented results are for θ = 40°.
A single spiral was the main characteristic in the outflow of the spiral graft and a double or triple spiral in the outflow of the control.
The maximum in-plane velocity (perpendicular to flow direction) at cross-flow planes 1 – 4 was constantly higher for the spiral graft model.
The total circulation in cross-flow planes 1 – 4 was higher for the spiral graft model particularly for increased Reynolds.
Helicity in the volume between cross-flow plane 1 and 4 was higher for the spiral model.
The pressure drop over length from the graft inlet to cross-flow plane 4 was reduced for the non-spiral graft model.
The wall shear stress (WSS) was examined in proximal and distal locations of the floor and toe wall centrelines. The WSS was higher for the spiral graft model in all tested locations.
The results from θ = 20°, 60°, 80° were comparable.
The flow pattern generated by the spiral graft was related to less flow separation, stagnation and instability than that induced by the control graft. The increased in-plane velocity, circulation and helicity of the spiral device showed increased in-plane mixing, which has been reported to protect endothelial function. Pressure drop is not desirable. The detected difference in pressure loss can be assumed negligible because the physiologic pressure is in the range of 1 – 20 × 104 Pa. Increased WSS is considered atheroprotective, although this may not apply in the proximal floor where the blood impinges abnormally on the wall of the host vessel.
The spiral graft was able to reintroduce a single spiral pattern in its outflow, associated with flow coherence downstream of the host vessel and high intensity cross-flow phenomena. Such local haemodynamics are known to prevent neointimal hyperplasia and thrombosis. These results support the hypothesis that spiral grafts may improve the patency rates in patients.
Spiral Laminar Flow, SLF, is the natural flow pattern found in healthy arteries. Blood leaves the left ventricle of the heart with a distinctive single spiral flow pattern and is propagated within the arterial system by the spiral configuration of the arterial luminal layers. SLF reduces static wall pressures at the intimal layer and, if destroyed, the severity of arterial disease and the tendency towards myointimal hyperplasia is greater. The Spiral Flow Peripheral Bypass Graft (Vascular Flow Technologies) reintroduces SLF at the distal anastomosis by a novel design at the distal end. To verify the advantages of this design, a series of peripheral bypass procedures using the graft were reviewed.
A retrospective multicentred, structured study of 72 patients who received the Spiral Flow Graft for peripheral bypass between February 2010 and February 2013 was performed. There were 61 males and 11 females, in which 75 bypasses were constructed; 68% were above knee and 32% were below knee. In all cases, the Fontaine Classification was 2b (severe claudication) or higher. Using duplex ultrasound and Computed Tomographic Angiography (CTA), all patients were scored as level C or D suitable for surgical revascularization according to the TASC IIb morphological stratification guidelines. In all cases the patients received general or epidural anaesthesia and antibiotic prophylaxis. Low molecular heparin was administered postoperatively out to 12 weeks.
Technical success at implantation was achieved in all 75 cases. The maximum and minimum follow-up was 38 months and 2 months respectively. There were no amputations in the limbs implanted with the Spiral Flow Graft and no cases of peri-operative bleeding or infection. There were 2 deaths due to serious comorbidities in this high-risk group of patients. Risk factors for vascular disease and indications for surgery were similarly distributed in the above knee and below knee bypasses. Primary patency rate was 85% and secondary patency 96%. 8 of 11 occlusions were successfully reopened with the use of thrombolysis, percutaneous angioplasty or open surgical revision. There were 3 permanent graft occlusions.
We implanted the Spiral Flow Peripheral Vascular Graft in 72 patients with peripheral occlusive arterial disease. The unique SLFTM technology is based on a renewed understanding of blood flow patterns in the healthy arterial system, the evidence of which is well documented. The mid-term results from this multicentre series of femoro-popliteal bypass procedures using the Spiral Flow Bypass Graft are encouraging.
Prosthetic graft failure is a normal tissue response to an abnormal flow environment. Endothelial cells at the anastomosis are sensitive to non-laminar flow environment (turbulence, stagnation, low shear stress, increased oscillatory index). These cells respond by signalling neo-intimal hyperplasia thus promoting failure. Results with prosthetic AV access grafts are far from ideal. We decided to use the Spiral flow graft for AV access based on early encouraging reports.
Patients and methods
This is a retrospective review of all cases that had Spiral Flow graft placement for AV access in the upper extremities.
From January, 2012 – January, 2014, 38 Spiral Flow™ AV Access Grafts (Vascular Flow Technologies Ltd) were placed in 37 patients.
The mean age was 61 years (range 42-88 years); 47% (18) were male. Patients presented with the following comorbidities: Diabetes: 25 (66%); Hypertension: 33 (87%); CAD: 8 (21%); CHF: 7 (18%); CVA: 7 (18%); PVD: 8 (21%).
Grafts were implanted as: Upper arm: 24; Forearm: 11; Chest wall: 3
The mean follow-up was nine months. 15 patients completed 12 months follow up. There are 20 grafts (53%) currently in use. Three grafts were removed for infection, 3 grafts were ligated for severe steal and 1 graft was ligated for severe arm swelling. Seven patients are deceased, all with their grafts patent.
Complications were as follows: Graft infection: 3 (8%); Significant Steal: 3 (8%); Thrombosis: 7 (18%); Venous stenosis: 3 (8%); Seroma: 4 (10%); Wound complications: 3 (7%); Venous hypertension: 7(18) and Pseudo-aneurysm: 0
Overall patency (%) results at 12 months are as follows:
|81% ± 9||83% ± 9
Spiral Flow Grafts are a valid and successful option for AV access. Early results are encouraging and tend to be better compared to standard straight ePTFE and heparin bonded grafts.
This may be explained on the basis of improved hemodynamics created by the spiral laminar flow.
Advantages of spiral flow laminar flow stability
–Spiral flow preserves laminar flow through a stenosis better reducing turbulent kinetic energy
Why a spiral flow graft?
- Intimal hyperplasia at the distal anastomosis is a frequent reason for graft failure.
- Development of intimal hyperplasia is a reaction of the blood vessel to abnormal flow patterns
- By inducing normal, spiral flow the development of intimal hyperplasia can be prevented
Patients and Methods
Phase 1 Study using 6 mm ringed ePTFE SLF graft (Vascular Flow Technologies Ltd). Spiral inducer at distal end to induce spiral flow at distal anastomosis.
39 Patients from 8 centres in Benelux
Study inclusion 02/06- 10/07; 5 year follow-up till 07/2013
- 73 % male, 27% female
- 59% above knee, 41% below knee
- 57% CLI, 43% Claudication
- 13% diabetics
- 43% current smokers
In 10 random patients the presence of spiral laminar flow at 3-6 months was assessed. All showed the distinctive flow pattern.
The five year cumulative patency rates were 62% above knee and 52% below knee.
- The phase 1 study showed that implantation of the Spiral Flow graft is feasible and safe.
- The Spiral Flow graft induces Spiral Laminar Flow at the distal anastomosis
- The 5 year results are encouraging compared to published literature
- Other products incorporating Spiral Laminar Flow technology are in development
Although, the preferred method to create an access is native AV fistula, there is still a significant number of patients where this is not feasible. AV access grafts are used in those patients and their patency rates are far from being ideal requiring frequent interventions to maintain their use. Their failure is usually related to stenosis of the venous outflow due to intimal hyperplasia, near the venous anastomosis of the graft. Neo-intimal hyperplasia may, in part, be a normal cellular response to an abnormal (turbulent) flow environment created by the AV access. Studies have shown that, Spiral laminar flow is the normal pattern of flow in most of the large and medium sized vessels in vivo. The Spiral flow graft has a design that creates a more natural spiral laminar flow at the venous end that is a hypothetically a more friendly hemodynamic environment thus reducing intimal hyperplasia and graft failure. We here report the early results of the largest available series of using the graft in AV access.
Retrospective review of all cases using the Spiral Flow graft for AV access in our institution, Jan 2012 to Jan 2014. Patients selected had no suitable superficial veins for native AV fistula. Patient demographics and comorbidities were recorded. Kaplan Meier curve analysis was used to calculate primary, assisted primary and secondary patency rates in comparison to historic controls of straight ePTFE and heparin bonded grafts for the same indication in our institution. Complications were also recorded.
A total of 38 cases were included. The access site was the arm (24), the forearm (11), and chest wall (3). Two thirds were females, mean age of 60 years and mean follow up of 8 months. At 12 month, the primary, assisted primary and secondary patency rates were 73%, 73% and 79%, respectively. Complications included 4 graft infections; 3 severe steal syndrome, 4 seromas and 2 arm swelling. There was only 1 early graft failure. There was only one early graft failure in less than 30 days in a patient with known hypercoagulable state who was not therapeutic on anticoagulation.
| ||Primary||Primary assisted||Secondary
|Spiral AVG||78 ± 8||73 ± 8||79 ± 8
|Heparin banded||56 ± 8||60 ± 8||59 ± 8
|Standard ePTFE||38 ± 10||47 ± 10||66 ± 11
12 month patency rates
Spiral flow grafts are a valid and successful option for AV access. One year results tend to be significantly superior to using straight ePTFE and heparin bonded grafts. This may be explained on the basis of the hemodynamic environment created by the spiral laminar flow and may be a significant contribution to preventing neointimal hyperplasia and hence AV access graft failure.
Summary of presentation
Spiral Laminar Flow (SLF) exhibits biological advantages:
- Holds cellular components in the centre of the flow
- Reduces near wall kinetic energy turbulence
- Reduces pressure drops across arterial branch points
- Should result in reduced downstream disease progression
A registry series experience using the Spiral Flow PV Graft between Feb 2011 and April 2012
- 17 implanted
- 73% male / 27% female
- Mean age at operation 67.7 (47.6 to 91.3) years
- 47% diabetic
- 30% right leg / 70% left leg
- 47% severe claudication / 53% critical ischemia
- 65% above knee popliteal
- 18% below knee popliteal with vein cuff
- 17% tibial vessels with vein cuff
1 x ‘Y’ graft onto distal limb of posterior tibial artery
1 x common femoral artery to contralateral distal anterior tibial artery
2 x common iliac transobturator to the above knee popliteal artery
Doppler ultrasound review
SLF observed at distal anastomosis and all run-off vessels in all cases in all post-op and subsequent scans.
Results at April 2012
- Primary patency rate: 93% at mean follow-up 4.47 (0 to 12.2) months
- Secondary patency rate: 100%, single graft, occluded 5.5 months post-op was successfully thrombolysed; re-occluded three months later, thrombolysed and angioplasty to the tibia-peroneal trunk, patient warfarenised and still patent.
Early results are encouraging with SLF PV grafts showing good primary patency rates.
More data required on the performance of the Spiral Flow PV Graft bench marked against conventional grafts.